I agree. I definitely stifle myself online more than I might in a small in-person group, or even a large group, for fear of negative reactions.

For me, it's got nothing to do with anonymity or some possible later repercussion; rather, it's being sensitive to short-term feedback. Effectively, the bandwidth of human communications through the internet is low and error-prone, and hence stressful for me to get my thoughts across. (It doesn't help that long-form replies -- which help me explain my ideas better -- have been grossly devalued.)

Sadly, it's gotten worse in the last few years -- perhaps due to Facebook, or perhaps due to societal changes that opened the door to mediums like Facebook.

I seem less and less capable of growing that thick skin that people always talk about...